1. Field of the Invention
The invention relates to a fuel injection control apparatus of an internal combustion engine, and more specifically, to a fuel injection control apparatus and fuel injection control method of an internal combustion engine, which can improve emissions by simultaneously reducing particulate matter (smoke), nitrogen oxides (NOx), and hydrocarbons (HC).
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-2002-295277 and Japanese Patent Application Publication No. JP-A-10-122015, for example, describe fuel injection control apparatuses of an internal combustion engine which are provided with a fuel injection valve that injects fuel directly into the combustion chamber. These control apparatuses aim to increase the temperature of a catalyst when the engine is cold started by performing a first fuel injection and spark igniting the injected fuel during the compression stroke, and performing a second fuel injection during the expansion stroke.
With these technologies, however, if the injection timing is advanced, as shown in FIG. 11, the period before the exhaust valve opens becomes longer so the amount of unburned fuel decreases which in turn results in less HC. On the other hand, the temperature in the cylinder is high so combustion takes place rapidly. As the combustion temperature rises, so too does the amount of NOx. Further, when the fuel is combusted without being sufficiently mixed with air, the amount of smoke increases. FIG. 11 is a conceptual diagram showing the relationship between the start timing of the second injection and emissions.
On the other hand, if the injection timing is retarded, the period before the exhaust valves open becomes shorter, which results in unburned fuel being exhausted, thus increasing the amount of HC. Further, the temperature in the cylinder is low so combustion takes place slowly. As a result, the combustion temperature drops so the amount of NOx decreases. In addition, the mixture of fuel and air is promoted which improves combustion and thus reduces the amount of smoke.
Thus, advancing the second injection timing during the expansion stroke reduces HC but increases smoke and NOx, while retarding that injection timing reduces smoke and NOx but increases HC. That is, smoke, NOx, and HC were unable to be simultaneously reduced. Therefore, a fuel injection control apparatus of an internal combustion engine was desired that could improve emissions by simultaneously reducing smoke, NOx, and HC.